1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Conventional wireless communication systems include one or more base stations, which may also be referred to as access points or node-Bs or access networks, for providing wireless connectivity to one or more mobile units, which may also be referred to using terms such as user equipment, subscriber equipment, and access terminals. Exemplary mobile units include cellular telephones, personal data assistants, smart phones, text messaging devices, laptop/notebook computers, desktop computers, and the like. Each base station may provide wireless connectivity to one or more mobile units, such as the mobile units in a geographical area, or cell, associated with the base station. For example, a base station may provide wireless connectivity to mobile units located in a cell according to a Universal Mobile Telecommunication System (UMTS) protocol.
In operation, each mobile unit maintains a wireless communication link, or leg, with one or more base stations. The wireless communication link typically includes one or more uplink and/or downlink channels for transmitting data and control information. Versions of the UMTS protocol prior to version 6 implement uplink and downlink dedicated channels (DCH) for transmitting data and/or control information between the mobile units and the base stations. A dedicated physical control channel (DPCCH) carries the DCH control information, such as pilot bits, transmit power control (TPC) bits, transport format combination information (TFCI), and the like that may be used on the uplink and/or downlink DCH. The DPCCH includes dedicated fields for carrying the DCH control information. A dedicated physical data channel (DPDCH) carries the DCH data.
Version 6 of the UMTS protocol includes many enhancements over previous versions of the UMTS protocol, some of which are intended to provide more efficient support for packet-switched networks. The enhanced dedicated channel (E-DCH) is an enhancement of the dedicated channel (DCH) that may provide more efficient support for the transmission of packet-switched data over the uplink. The High-Speed Downlink Shared Channel (HS-DSCH) may increase the efficiency of the packet-switched data transmission in the downlink as compared to the dedicated channels. On the physical layer, E-DCH data is transmitted over an enhanced dedicated physical data channel (E-DPDCH).
Additional physical control channels have also been included in Version 6 of the UMTS protocol, at least in part because E-DCH introduces new physical layer (PHY) and medium access control (MAC) layer functionalities, such as hybrid ARQ (HARQ) and dynamic scheduling. For example, the following physical control channels may be available in UMTS, version 6:                An uplink enhanced dedicated physical control channel (E-DPCCH), which may be used for signaling E-DCH transport format combination information (E-TFCI), a retransmission sequence number (RSN) that mobile units may use on the E-DPDCH, and a happy bit.        A downlink HARQ Indicator Channel (E-HICH), which may carry ACK/NACK information for the hybrid ARQ protocol.        A downlink Absolute Grant Channel (E-AGCH), which may be used for signaling the absolute grant (AG), which is a product of the scheduling process.        A downlink Relative Grant Channel (E-RGCH), which may be used for the signaling of relative grants (RG), which is a product of the scheduling process.These channels typically consume uplink and/or downlink resources. Consequently, usage of E-DCH control channels may reduce the efficiency of the wireless communication system and/or the capacity available to the uplink and downlink data channels. The decreases in efficiency and/or data traffic capacity may be especially important when a relatively small amount of data is sent (compared to the amount of control information) and the signaling overhead becomes significant relative to the amount of transmitted data. The presence of both DCH and E-DCH data and control channels may also increase interference levels in the wireless communication system.        
Introduction of the enhanced data channel and associated control channels may make portions of existing, or legacy, channels redundant. For example, the E-DCH may be used to transmit data and/or control signals over the uplink and the HS-DSCH may be used to transmit data and/or control signals over the downlink. Consequently, the DCH (and associated data and/or control channels) may not be used to transmit data and/or portions of the control information. However, the DPCCH may still be utilized to transmit pilot signal information. Thus, the transport format combination information fields of the DPCCH may become redundant. Transmitting the redundant field(s) may increase the overhead associated with the wireless communication link, which may decrease the efficiency of transmissions over the wireless communication link and/or the capacity of the wireless communication link.